The present disclosure relates to a vitreous silica crucible for pulling silicon single crystals, and more particularly, to a structure of an opaque vitreous silica layer in a vitreous silica crucible.
A vitreous silica crucible is used to manufacture silicon single crystals. In Czochralski method (CZ method), polysilicon is put into a vitreous silica crucible, heated and melted to prepare a silicon melt, a seed crystal is then dipped into the silicon melt, and a silicon single crystal grows by gradually pulling up the seed crystal while rotating the crucible. To manufacture high-purity silicon single crystals for semiconductor devices, it is required that silicon single crystals should not be contaminated due to elution of impurities contained in a vitreous silica crucible, and the vitreous silica crucible should also have a heat capacity enough to easily control the temperature of a silicon melt therein. For this reason, a vitreous silica crucible having a double-layered structure is being popularly used, which is configured with an opaque outer layer containing a plurality of micro-bubbles and a transparent inner layer not containing a bubble (see Patent Document 1). Also, another vitreous silica crucible having a double-layered structure is in use, in which an outer layer of the crucible is formed of natural quartz to increase the strength of the crucible and an inner layer of the crucible contacting a silicon melt is formed of synthetic silica to substantially reduce the inclusion of impurities (see Patent Document 2). To increase single crystallization rate, yet another vitreous silica crucible was also proposed, in which a bubble content of a transparent glass layer at a sidewall part is set to 0.5% or less and a bubble content of a transparent glass layer at a bottom part is further reduced to 0.01% or less (see Patent Document 3).